The invention relates to an apparatus for regulating axial compressors by adjusting two rows of guide vanes arranged successively in flow direction. The guide vanes in their neutral position (vane position at 0.degree. deviation from the direction of the rotor axis) are adjusted parallel to the rotor axis and are each pivotally arranged around a vane rotary axis, so that the guide vanes of the front (first) row, in flow direction, are adjustable relative to the guide vanes of the following row, in flow direction (second flow), by means of an adjustment ring or similar device. The first row has a leading angle of incidence, and to the second row of guide vanes is assigned a second angle of incidence, being at a certain ratio to the first mentined angle of the first row of guide vanes.
The entrance stage plays a special part in regulating axial compressors by adjusting the guide vanes. While up until now the flow direction toward the guide vanes between each two carrying wheels has been changed by regulating the preceding steps, this flow direction has remained always axial for the entrance guide wheel. Beginning with a certain angle of adjustment, the flow in the entrance guide wheel becomes discontinuous, which impairs the effect of the following carrying wheel. A calculation of the aditional losses in the entrance guide wheel and in the first carrying wheel clearly shows that, subsequent to the discontinuity of flow in the entrance guide wheel, a positive regulating effect in counter-torque direction is restrained, a regulating gap occurs in the partial-load region where the flow guidance is smaller than it was prior to flow discontinuity, the effectiveness of the first stage is greatly impaired, and the guide vanes are exposed to strongly fluctuating forces.
In conventional turbo-compressors, the first row of vanes forms the entrance guide wheel. In contrast to the other guide wheels, which are between each two carrying wheels, a special position may be allowed said entrance guide wheel: the adjustment region for the vanes of the entrance guide wheel is preferably only large enough, within the normal regulating region of the machine, for the flow discontinuity not to occur. The adjustment characteristic curve, valid for a certain initial whirl produced in the entrance guide wheel of the first carrying wheel, may be exploited between the discontinuity and absorption boundary.
The velocity of the flow towards the vanes of the entrance guide wheel is always essentially axially aligned.
When the vanes of the entrance guide wheel are shifted by shifting the guide vane while the compressor is regulated, they must always guide the flow from the axial direction into another direction, partially in the direction of rotation of the compressor rotor (co-torque) or partially in the opposite direction (counter-torque).
As mentioned, when a certain angle of the oncoming flow is exceeded, the flow to the profile becomes discontinuous.
In one regulating direction, which extends into the partial-load region, such exceeding of the flow-discontinuity angle causes additional losses which are initially not noticeable externally at the compressor stage or in the total compressor. Indeed, the increase of the losses may be compared to choking, an effect which is not desired, but which, however, is effective in the desired regulating direction.
If, however, regulation occurs in the other direction, i.e., in the excess region, the discontinuity of the flow is externally noticeable by a sudden reverse regulating effect. Instead of the compression ratio of the massive through-put through the machine being increased, a counter-effect occurs, beginning at a certain boundary angle. Additional losses occur not only in the entrance guide wheel but, above all, in the successive carrying wheel, through the detached flow regions which are very turbulent, so that the desired effect is not only voided, but is even turned into its opposite.
Previously it was sometimes customary to shift the vanes of the entrance guide wheel in muti-stage machines by a smaller angle than, for example, the vanes of the first center guide wheel which is arranged between the first and second carrying wheel.
Apparatus for differentiated coupled shifts of two rows of guide vanes, interconnecting in flow direction of a turbo compressor, are known (DE-OS No. 24 03 113; DE-OS No. 25 02 986). In these apparatus, the rows of guide vanes are arranged successively and axially to the direction of the rotor axis. The centers of rotation of the guide vanes which are, in each case, arranged successively in flow direction, lie on the line extending parallel to the rotor axis.
However, in this type of arrangement of the vanes, it is not possible, with a maximal flow guide in one or the other regulating sense, to achieve an aerodynamically optimal gap between the cooperating vanes or an optimal flow.
Furthermore, apparatus for regulating turbo-compressors by shifting guide vanes are known, in which the guide vanes are not rigidly formed but have an articulated profile. This may cause very advantageous aerodynamic conditions. Constructions of that type are described in the NASA reports TND-3823 of January 1967 and CR-54534 PWAFR-2112 of Aug. 2, 1968 of the National Aeronautics and Space Administration, Washington, D.C.
The following constructions, for example, are known from these reports:
Arrangement of two-piece vanes, consisting of a rigid fin and a controlled rudder.
A rudder, provided with a gap.
A fin with a curved rear element.
A rudder dissembled into several elements.
These multi-joined vanes produce the desired effect; however, they are of a complicated constructional design.